Amherst College has reaffirmed a 30-year ban on fraternities and sororities including off-campus underground organizations in the wake of a federal investigation of sexual assault cases there.

The Board of Trustees of the private school about 90 miles west of Boston said in an email Tuesday that students who join "off-campus fraternities and sororities, and fraternity-like and sorority-like organizations" are subject to suspension or expulsion, a policy that effect July 1.

But despite being one of six Massachusetts institutions and 55 U.S. colleges under a current federal investigation over the handling of sexual assault complaints, the Amherst administration adamantly defended the timing of the move as pure coincidence.

A committee made up of students, faculty and staff recommended in January 2013 that the board review Greek life along with a range of issues at the college, chief student affairs officer Suzan Coffey said.

"The committee did not find that there was a correlation between sexual assault and frats and sororities," Coffey said. "This decision was made to resolve the ambiguous nature of these different social structures and help bring them above ground so they can work with administrators."

The decision is an effort to create a more productive and healthy social scene at Amherst and not a reaction to any sexual assault allegations, she said.

Students will be expected to uphold the policy through the college's honor code. Moving forward, the college said it hopes to work with the students to create organizations that foster the values the students have voiced.

In 1984, soon after the college allowed women to attend, on-campus fraternities were barred after a trustee subcommittee determined that Amherst "can be better without fraternities than it can with them." As a result, some Greek organizations took on what the trustees called underground status. Other small liberal arts schools such as Middlebury College, Bowdoin College and Williams College also have tried to ban Greek organizations.

An estimated 90 students out of an 1,800-member student body at Amherst participate in these organizations. The three known underground fraternities active at Amherst are Chi Psi, Delta Kappa Epsilon and OT.

The president of Chi Psi, junior William Kamin, said he is disappointed by the decision and thinks it will hurt rather than benefit student life. He said respect for women is something especially stressed at the Chi Psi house.

"The amount of trust in fraternities has allowed men at the college to be more open, honest and vulnerable about what they have gone through and are going through," Kamin said. "It has taught guys about what it means to be a man, and a good man at that."